Lead acid electrochemical cells which are otherwise known as “lead-acid batteries” are commonly used to store and deliver electrical energy. For example, lead acid electrochemical cells are normally employed in vehicles (e.g. cars, trucks, boats, aircraft, and the like) for ignition, lighting, and other related purposes.
Conventional lead-acid electrochemical cells include electrically-conductive positive and negative current collectors typically manufactured in the form of foraminous (porous) metallic grids which are manufactured from a lead alloy or elemental lead (99.90%-99.990% purity lead) as noted in U.S. Pat. No. 3,951,688. The individual current collectors may be planar (flat) in configuration or spirally-wound. Regardless of form, both the positive and negative current collectors (e.g. grids) are coated with a paste composition that is directly deposited onto both sides of the current collectors during cell production. As a result, positive and negative “plates” are formed from the pasted current collectors. The positive and negative pastes are typically produced from one or more particulate lead-containing compositions which may consist of, for example, lead (Pb) or lead compounds (e.g. oxides such as PbO, PbO2 and/or Pb3O4 “red lead” The selected lead-containing compositions are then combined with a paste “vehicle” (e.g. water) and various other optional ingredients including sulfuric acid. Other additives of interest comprise expander materials as discussed in U.S. Pat. No. 4,902,532 which include barium sulfate, carbon black, and lignosulfonate. The expander materials are primarily used in connection with the negative paste as discussed further below.
The paste composition positioned on the positive current collector to form the positive plate in an electrochemical cell is typically characterized as the “positive paste”, while the paste composition located on the negative current collector to produce the negative plate is known as the “negative paste”. Further information regarding these items and other characteristics of battery paste compositions in general are presented in U.S. Pat. No. 4,648,177 which is incorporated herein by reference. Likewise, methods of applying the paste compositions listed above to the positive and negative current collectors are specifically discussed in U.S. Pat. Nos. 3,894,886; 3,951,688 and 4,050,482 which are also incorporated by reference.
In 1915, in the U.S. Pat. No. 1,148,062, a process is described for the recovery of lead from exhausted batteries. According to this patent, extracted spent battery pastes are transformed into lead oxides by calcinations and desulfurization. However, the oxides produced are not of high purity.
According to the U.S. Pat. No. 4,222,769, an extracted spent battery paste is desulfurized and then transformed into metallic lead by roasting in the presence of a carbon reducing agent.
In U.S. Pat. No. 4,769,116, a paste is obtained from exhausted lead-acid batteries and treated with sodium hydroxide to produce a solution of sodium sulfate and a desulfurized paste. Pure metallic lead is further recovered from the desulfurized paste by electrowinning.
U.S. Pat. No. 5,211,818 discloses a process wherein the paste sludge resulting from the exhausted batteries is treated with a solution of ammonium sulfate and the metallic lead constituent is recovered by electrowinning.
International Publication No. WO99/44942 discloses a process of producing lead monoxide from spent lead batteries using fluxing agents and an organic reducer in a calcinations step at a temperature of 400° C.-450° C.
As can be noticed from the brief review, in most of the prior references, the recovered lead from exhausted batteries is in its metallic form and, consequently, has to be further converted to the respective oxides.